Increasing the amount of data recorded on a given surface area of a recording medium, i.e., a tape, is a continuing endeavor of manufacturers. It is essential to the goal of increased data densities to store each magnetic data signal on the smallest possible surface area of the recording medium while retaining the capability of reliably recovering the data stored on the recording medium.
An impediment to accurate recording and recovery of the data stored on narrow, closely spaced, tracks is lateral wander of the recording medium as it moves longitudinally over the recording head. As data tracks are narrowed and placed closer together, the spacing between the tracks cannot accommodate the lateral wander of the recording medium, and consequently a transducer initially aligned to one track may become misaligned as the recording medium is transported past the transducer. Tape wander may take the form of excursions of comparatively large magnitude, both longitudinally to and laterally with respect to the transducer, especially during stopping and starting conditions, but also during steady state transport. These large excursions make accurate alignment of the recording head relative to the recording medium particularly difficult. Because of the above mentioned excursions and the non-uniformity of tape movement, accurate alignment of the recording head relative to the recording medium becomes increasingly important as track density increases and the tracks are arranged closer together.
To compensate for lateral tape wander and in an effort to maintain recording head position relative to the recording medium, servo systems have been developed which physically manipulate the recording head position in response to that of the recording medium as it is transported past the head. These servo systems use servo tracking centering signals prerecorded on a recording medium as a reference for the recording head and continuously adjust the position of the recording head relative to any selected one of several long tracks of servo signals prerecorded on the tape.
Although these servo tracking systems allow for significant reduction in the track width and the space between the tracks on the recording medium, the ability of manufacturers of magnetic storage systems to make further reductions in the track width, and the space in between the tracks on the record member, is limited by the ability of transducers to accurately record servo-tracking signals which are narrower and spaced closer together.
Some transducers for writing servo tracking centering signals on a recording medium use a write core which sequentially writes the servo tracking signals for each track by embedding the sensoring signals on the recording medium one track at a time. Consequently, the servo system is required to accurately, and with high precision, position the transducer on each track as the write core records the tracking signal for that track. Due to the excursions of the recording medium relative to the transducer head, both laterally and longitudinally, which occur during stopping and starting as well as steady state transport of the recording medium, since the tape is under a tension as it is transported lengthwise, it is difficult and impractical for a system using a single track write core to accurately align servo tracking centering signals longitudinally and laterally as the number of tracks on the recording medium increases.
In addition to the difficulties encountered in accurately positioning the single track transducer for recording the servo tracking centering signals due to lateral excursions of the recording medium, and longitudinal offset due to repeated transport of the storage media past the transducer, expanded writing centering signals increases as the number of tracks increase. This increase occurs because the entire length of the recording medium must be transported past the transducer as the centering signals for each individual track of the recording medium is recorded. For storage media having a large number of tracks, the time required to repeatedly transport the storage media past the transducer and record the centering signals becomes excessively large.
Multi-gap transducers are known which are capable of reading or writing signals from a plurality of different data tracks simultaneously. However, these transducers have a number of characteristics which prevent them from being truly effective or desirable for recording multiple-track servo-tracking signals for high density data storage. For example, stacked-core transducers have multiple cores which are magnetically isolated from one another and have gaps which are spaced apart by a distance of at least one track width. These transducers are relatively complex in construction and thus are costly to manufacture due to the number of cores and windings which make up the transducer. Additionally, the physical dimensions of each of the cores which form the respective gaps of each stacked-core transducer limit the number of cores which can be stacked for a particular width of tape due to the thickness of material required to give the legs of the core structural strength and a geometry for generating flux in the recording medium. The width of the respective cores added to the thickness of the magnetic insulator between each core essentially prevents the use of stacked-core transducers to record adjacent, closely spaced tracks.
In an improved process, a special recording head is used which has "slots" cut into the write head corresponding to the spacing between the bursts in the recorded servo signal pattern. Since no signal is written underneath the region corresponding to the slots, the "above" center line burst patterns for all written tracks can be written in a single pass across the media, then the "below" center line burst patterns for all written tracks can be written in a subsequent pass. The match between the signal characteristics, which is a critical part of the subsequent usage of the signals for positioning, is fair between the "above" and "below" burst patterns, since they are written by the same write head, but some differences can be observed due to the fact that they were written in two separate passes across the media, and possibly the use of write operations in different directions across the recording medium.
In an alternative process, two separate slotted write heads can be implemented, again with the slot size corresponding to the desired space in between the bursts in the recorded pattern. However, signal characteristics of bursts written by two separate write heads will not always match well, so that an error in decoding position information will result. Most of the aforementioned systems require multiple passes over the media in order to write the desired servo pattern. In addition to the signal mismatch due to multiple passes, the processing time required to write the pattern also increases.